1. Field of the Invention
The present invention relates to a backlight unit, and more particularly, to a flat panel fluorescent lamp and fabricating method thereof, by which discharge uniformity is enhanced.
2. Discussion of the Related Art
Generally, a cathode ray tube (CRT), one of various display devices, has been used as a monitor of a measuring equipment, information terminals, or the like, as well as televisions. Yet, large size and heavy weight of the CRT fail to meet the demand for compactness and lightweight of electronic products.
There are limitations on the weight and size of the CRT which is contrary to the trend of compactness and lightweight of various electronic products. Hence, there are various display devices expected to replace the CRT such as LCD (liquid crystal display) device using optical electric field effect, PDP (plasma display panel) using gas discharge, ELD (electroluminescent display) using electroluminescence, and the like. Specifically, many efforts to research and develop the LCD are underway.
In order to replace the CRT, the LCD, which is advantageous in compact/slim size, lightweight, low power consumption, and the like, has been widely researched and developed. The LCD has been developed enough to play a role as a flat panel display and is adopted as a monitor of a desktop computer, a wide information display device, and the like, as well as laptop computers. Hence, the demand for the LCD keeps rising.
The LCD is mostly a light-receiving device that displays an image by controlling an external incident light, thereby needing a separate light source for applying a light to an LCD panel, i.e., a backlight unit. The backlight unit used as a light source of LCD is categorized into an edge-light type and a direct-light type according to an installation location of a lamp unit.
EL (electroluminescence), LED (light-emitting diode), CCFL (cold cathode fluorescent lamp), HCFL (hot cathode fluorescent lamp), EEFL (external electrode fluorescent lamp), or the like can be used as the light source of the LCD. The CCFL, which is advantageous in long endurance, less power consumption, and thin slimness, is mainly used for a wide-screen color TFT LCD.
A CCFL light source uses a fluorescent discharge tube having Hg gas (with Ar, Ne, etc.) sealed therein at a low temperature in order to utilize a penning effect. Electrodes are formed at both ends of the tube. A cathode has a plate shape. When a voltage is applied to the electrodes, charged particles within the discharge tube collide with the cathode to produce secondary electrons. The secondary electrons excite neighbor elements to form plasma.
The excited elements irradiate strong UV-light and the UV-lights excite a fluorescent substance to irradiate a visible light.
In the edge-light type backlight unit, a lamp unit is provided to one side of a light-guide plate. And, the lamp unit consists of a lamp emitting light, a lamp holder inserted in both ends of the lamp to protect the lamp, and a lamp reflector enclosing an outer edge or circumference of the lamp to have one side fitted in a lateral side of the light guide plate to reflect the light emitted from the lamp toward the light guide plate.
The edge-light type backlight unit having the lamp unit provided to one side of the light guide plate is mainly applicable to a small-size LCDs, such as a laptop computer, a desktop computer, and the like. Hence, the edge-light type backlight unit provides excellent light uniformity, long endurance, and advantage of slimness of LCD.
The direct-light type backlight unit, which has been developed to cope with a wide-screen LCD over 20 inches, arranged a plurality of lamps in one line on a lower side of a diffusion plate to directly illuminate a front side of an LCD panel.
The direct-light type backlight unit has light efficiency higher than that of the edge-light type backlight unit, thereby being mainly adopted by a wide-screen LCD requiring high brightness.
FIG. 1 is a perspective diagram of a direct-light type backlight unit according to a related art, and FIG. 2 is a perspective diagram of electrode-connecting wires connected between a light-emitting lamp and a connector.
Referring to FIG. 1, a direct-light type backlight unit according to a related art consists of a plurality of light-emitting lamps 1 having insides coated with a fluorescent substance to emit light, an outer case 3 to support the light-emitting lamps 1, and a plurality of light-diffusion means 5a, 5b, and 5c provided between a liquid crystal display panel (not shown in the drawing) and the light-emitting lamps 1.
The light-diffusion means 5a, 5b, and 5c prevent the shape of the light-emitting lamps 1 from appearing on a display surface of the liquid crystal display panel and provide a light source having a uniform luminosity distribution overall. In order to enhance a light-diffusion effect, a plurality of diffusion sheets and plates are arranged between the liquid crystal display panel and the light-emitting lamps 1.
A reflector 7 is provided to an inside of the outer case 3 to condense the lights emitted from the light-emitting lamps 1 on a display part of the liquid crystal display panel. This is to maximize efficiency of light use.
Each of the light-emitting lamps 1, as illustrated in FIG. 2, consists of a cold cathode fluorescent lamp (CCFL). Electrodes 2 and 2a are provided to respective ends of a tube. When power is applied to the electrodes 2 and 2a, the corresponding light-emitting lamp 1 emits light. Respective ends of the light-emitting lamp 1 are fitted in holes formed at respective sides of the outer case 3.
Electrode-connecting wires 9 and 9a for transferring external power for driving the corresponding lamp are connected to the electrodes 2 and 2a of the light-emitting lamp 1, respectively. The electrode-connecting wires 9 and 9a are connected to a separate connector 11 to be connected to a driver circuit. Hence, the connector 11 should be provided to each of the light-emitting lamps 1.
Namely, one electrode-connecting wire 9 connected to one electrode 2 of the light-emitting lamp 1 and the other electrode-connecting wire 9a connected to the other electrode 2a of the light-emitting lamp 1 are connected to one connector 11. One of the electrode connecting wires 9 and 9a is bent toward a rear side of the outer case 3 to be connected to the connector 11.
FIG. 3 is a cross-sectional diagram of a flat panel fluorescent lamp according to a related art.
Referring to FIG. 3, a flat panel fluorescent lamp unit according to a related art consists of an upper plate 21 formed of a transparent material, a fluorescent layer 22 formed on a rear side of the upper plate 21, a lower plate 23 provided to leave a predetermined gap from the upper plate 21, a plurality of ribs 24 formed on the lower plate 23 having a predetermined distance from each other, a plurality of electrodes 25 enclosing a plurality of the ribs 24, respectively, a dielectric layer 26 covering each surface of the electrodes 25, and a peripheral wall 27 supporting both edges of the upper and lower plates 21 and 23 to provide the gap between the upper plate 21 and the lower plate 23.
A height of the peripheral wall 27 is greater than that of each of the electrodes 25, whereby electric discharge can occur between the electrodes 25.
In the above-configured flat panel fluorescent lamp of the related art, a plurality of the electrodes 25 are grouped into odd-numbered electrodes and even-numbered electrodes to be connected to an AC-power supply.
Consequently, electric discharge is produced between the odd-numbered electrodes and the even-numbered electrodes. Alternatively, a plurality of the electrodes can be grouped into a plurality of pairs of two neighbor electrodes to be connected to the same power supply.
In the related art flat panel fluorescent lamp, a plurality of the electrodes 25 protruding from the lower plate 23 produce plasma by AC type electric discharge, the plasma irradiates UV-light to excite the fluorescent layer 22 on the upper plate 21, and the excited fluorescent layer 22 irradiates a visible light outside the upper plate 21.
The gas employs a mixed gas with Xe as well as Hg.
The AC type electric discharge is performed in a manner of applying alternating polarities of power to the electrodes 25 coated with the dielectric layer 26.
A width and protruding height of the electrode 25 and the distance between the electrodes 25 are set in a manner of considering a gas pressure and electric discharge efficiency. For instance, the distance between the electrodes 25 is set smaller than 1 mm for electric discharge of the gas at a high pressure of several hundreds Torr.
The rib-type electrodes may be formed by printing. The dielectric layer 26 is to prevent the electrodes from being damaged by ions and to raise the discharge of the secondary electrons.
However, the related art flat panel fluorescent lamp has the following problems or disadvantages.
Namely, an acquisition rate of externally transmissive light is low and uniformity of electric discharge is reduced, whereby brightness and efficiency required for a wide-screen liquid crystal display device cannot be met.